<!doctype html><html lang="en">
 <head>
  <meta content="text/html; charset=utf-8" http-equiv="Content-Type">
  <title>Private Click Measurement</title>
  <meta content="width=device-width, initial-scale=1, shrink-to-fit=no" name="viewport">
<style data-fill-with="stylesheet">/******************************************************************************
 *                   Style sheet for the W3C specifications                   *
 *
 * Special classes handled by this style sheet include:
 *
 * Indices
 *   - .toc for the Table of Contents (<ol class="toc">)
 *     + <span class="secno"> for the section numbers
 *   - #toc for the Table of Contents (<nav id="toc">)
 *   - ul.index for Indices (<a href="#ref">term</a><span>, in §N.M</span>)
 *   - table.index for Index Tables (e.g. for properties or elements)
 *
 * Structural Markup
 *   - table.data for general data tables
 *     -> use 'scope' attribute, <colgroup>, <thead>, and <tbody> for best results !
 *     -> use <table class='complex data'> for extra-complex tables
 *     -> use <td class='long'> for paragraph-length cell content
 *     -> use <td class='pre'> when manual line breaks/indentation would help readability
 *   - dl.switch for switch statements
 *   - ol.algorithm for algorithms (helps to visualize nesting)
 *   - .figure and .caption (HTML4) and figure and figcaption (HTML5)
 *     -> .sidefigure for right-floated figures
 *   - ins/del
 *
 * Code
 *   - pre and code
 *
 * Special Sections
 *   - .note       for informative notes             (div, p, span, aside, details)
 *   - .example    for informative examples          (div, p, pre, span)
 *   - .issue      for issues                        (div, p, span)
 *   - .assertion  for assertions                    (div, p, span)
 *   - .advisement for loud normative statements     (div, p, strong)
 *   - .annoying-warning for spec obsoletion notices (div, aside, details)
 *
 * Definition Boxes
 *   - pre.def   for WebIDL definitions
 *   - table.def for tables that define other entities (e.g. CSS properties)
 *   - dl.def    for definition lists that define other entitles (e.g. HTML elements)
 *
 * Numbering
 *   - .secno for section numbers in .toc and headings (<span class='secno'>3.2</span>)
 *   - .marker for source-inserted example/figure/issue numbers (<span class='marker'>Issue 4</span>)
 *   - ::before styled for CSS-generated issue/example/figure numbers:
 *     -> Documents wishing to use this only need to add
 *        figcaption::before,
 *        .caption::before { content: "Figure "  counter(figure) " ";  }
 *        .example::before { content: "Example " counter(example) " "; }
 *        .issue::before   { content: "Issue "   counter(issue) " ";   }
 *
 * Header Stuff (ignore, just don't conflict with these classes)
 *   - .head for the header
 *   - .copyright for the copyright
 *
 * Miscellaneous
 *   - .overlarge for things that should be as wide as possible, even if
 *     that overflows the body text area. This can be used on an item or
 *     on its container, depending on the effect desired.
 *     Note that this styling basically doesn't help at all when printing,
 *     since A4 paper isn't much wider than the max-width here.
 *     It's better to design things to fit into a narrower measure if possible.
 *   - js-added ToC jump links (see fixup.js)
 *
 ******************************************************************************/

/******************************************************************************/
/*                                   Body                                     */
/******************************************************************************/

	body {
		counter-reset: example figure issue;

		/* Layout */
		max-width: 50em;               /* limit line length to 50em for readability   */
		margin: 0 auto;                /* center text within page                     */
		padding: 1.6em 1.5em 2em 50px; /* assume 16px font size for downlevel clients */
		padding: 1.6em 1.5em 2em calc(26px + 1.5em); /* leave space for status flag     */

		/* Typography */
		line-height: 1.5;
		font-family: sans-serif;
		widows: 2;
		orphans: 2;
		word-wrap: break-word;
		overflow-wrap: break-word;
		hyphens: auto;

		/* Colors */
		color: black;
		background: white top left fixed no-repeat;
		background-size: 25px auto;
	}


/******************************************************************************/
/*                         Front Matter & Navigation                          */
/******************************************************************************/

/** Header ********************************************************************/

	div.head { margin-bottom: 1em }
	div.head hr { border-style: solid; }

	div.head h1 {
		font-weight: bold;
		margin: 0 0 .1em;
		font-size: 220%;
	}

	div.head h2 { margin-bottom: 1.5em;}

/** W3C Logo ******************************************************************/

	.head .logo {
		float: right;
		margin: 0.4rem 0 0.2rem .4rem;
	}

	.head img[src*="logos/W3C"] {
		display: block;
		border: solid #1a5e9a;
		border-width: .65rem .7rem .6rem;
		border-radius: .4rem;
		background: #1a5e9a;
		color: white;
		font-weight: bold;
	}

	.head a:hover > img[src*="logos/W3C"],
	.head a:focus > img[src*="logos/W3C"] {
		opacity: .8;
	}

	.head a:active > img[src*="logos/W3C"] {
		background: #c00;
		border-color: #c00;
	}

	/* see also additional rules in Link Styling section */

/** Copyright *****************************************************************/

	p.copyright,
	p.copyright small { font-size: small }

/** Back to Top / ToC Toggle **************************************************/

	@media print {
		#toc-nav {
			display: none;
		}
	}
	@media not print {
		#toc-nav {
			position: fixed;
			z-index: 2;
			bottom: 0; left: 0;
			margin: 0;
			min-width: 1.33em;
			border-top-right-radius: 2rem;
			box-shadow: 0 0 2px;
			font-size: 1.5em;
			color: black;
		}
		#toc-nav > a {
			display: block;
			white-space: nowrap;

			height: 1.33em;
			padding: .1em 0.3em;
			margin: 0;

			background: white;
			box-shadow: 0 0 2px;
			border: none;
			border-top-right-radius: 1.33em;
			background: white;
		}
		#toc-nav > #toc-jump {
			padding-bottom: 2em;
			margin-bottom: -1.9em;
		}

		#toc-nav > a:hover,
		#toc-nav > a:focus {
			background: #f8f8f8;
		}
		#toc-nav > a:not(:hover):not(:focus) {
			color: #707070;
		}

		/* statusbar gets in the way on keyboard focus; remove once browsers fix */
		#toc-nav > a[href="#toc"]:not(:hover):focus:last-child {
			padding-bottom: 1.5rem;
		}

		#toc-nav:not(:hover) > a:not(:focus) > span + span {
			/* Ideally this uses :focus-within on #toc-nav */
			display: none;
		}
		#toc-nav > a > span + span {
			padding-right: 0.2em;
		}

		#toc-toggle-inline {
			vertical-align: 0.05em;
			font-size: 80%;
			color: gray;
			color: hsla(203,20%,40%,.7);
			border-style: none;
			background: transparent;
			position: relative;
		}
		#toc-toggle-inline:hover:not(:active),
		#toc-toggle-inline:focus:not(:active) {
			text-shadow: 1px 1px silver;
			top: -1px;
			left: -1px;
		}

		#toc-nav :active {
			color: #C00;
		}
	}

/** ToC Sidebar ***************************************************************/

	/* Floating sidebar */
	@media screen {
		body.toc-sidebar #toc {
			position: fixed;
			top: 0; bottom: 0;
			left: 0;
			width: 23.5em;
			max-width: 80%;
			max-width: calc(100% - 2em - 26px);
			overflow: auto;
			padding: 0 1em;
			padding-left: 42px;
			padding-left: calc(1em + 26px);
			background: inherit;
			background-color: #f7f8f9;
			z-index: 1;
			box-shadow: -.1em 0 .25em rgba(0,0,0,.1) inset;
		}
		body.toc-sidebar #toc h2 {
			margin-top: .8rem;
			font-variant: small-caps;
			font-variant: all-small-caps;
			text-transform: lowercase;
			font-weight: bold;
			color: gray;
			color: hsla(203,20%,40%,.7);
		}
		body.toc-sidebar #toc-jump:not(:focus) {
			width: 0;
			height: 0;
			padding: 0;
			position: absolute;
			overflow: hidden;
		}
	}
	/* Hide main scroller when only the ToC is visible anyway */
	@media screen and (max-width: 28em) {
		body.toc-sidebar {
			overflow: hidden;
		}
	}

	/* Sidebar with its own space */
	@media screen and (min-width: 78em) {
		body:not(.toc-inline) #toc {
			position: fixed;
			top: 0; bottom: 0;
			left: 0;
			width: 23.5em;
			overflow: auto;
			padding: 0 1em;
			padding-left: 42px;
			padding-left: calc(1em + 26px);
			background: inherit;
			background-color: #f7f8f9;
			z-index: 1;
			box-shadow: -.1em 0 .25em rgba(0,0,0,.1) inset;
		}
		body:not(.toc-inline) #toc h2 {
			margin-top: .8rem;
			font-variant: small-caps;
			font-variant: all-small-caps;
			text-transform: lowercase;
			font-weight: bold;
			color: gray;
			color: hsla(203,20%,40%,.7);
		}

		body:not(.toc-inline) {
			padding-left: 29em;
		}
		/* See also Overflow section at the bottom */

		body:not(.toc-inline) #toc-jump:not(:focus) {
			width: 0;
			height: 0;
			padding: 0;
			position: absolute;
			overflow: hidden;
		}
	}
	@media screen and (min-width: 90em) {
		body:not(.toc-inline) {
			margin: 0 4em;
		}
	}

/******************************************************************************/
/*                                Sectioning                                  */
/******************************************************************************/

/** Headings ******************************************************************/

	h1, h2, h3, h4, h5, h6, dt {
		page-break-after: avoid;
		page-break-inside: avoid;
		font: 100% sans-serif;   /* Reset all font styling to clear out UA styles */
		font-family: inherit;    /* Inherit the font family. */
		line-height: 1.2;        /* Keep wrapped headings compact */
		hyphens: manual;         /* Hyphenated headings look weird */
	}

	h2, h3, h4, h5, h6 {
		margin-top: 3rem;
	}

	h1, h2, h3 {
		color: #005A9C;
		background: transparent;
	}

	h1 { font-size: 170%; }
	h2 { font-size: 140%; }
	h3 { font-size: 120%; }
	h4 { font-weight: bold; }
	h5 { font-style: italic; }
	h6 { font-variant: small-caps; }
	dt { font-weight: bold; }

/** Subheadings ***************************************************************/

	h1 + h2,
	#subtitle {
		/* #subtitle is a subtitle in an H2 under the H1 */
		margin-top: 0;
	}
	h2 + h3,
	h3 + h4,
	h4 + h5,
	h5 + h6 {
		margin-top: 1.2em; /* = 1 x line-height */
	}

/** Section divider ***********************************************************/

	:not(.head) > hr {
		font-size: 1.5em;
		text-align: center;
		margin: 1em auto;
		height: auto;
		border: transparent solid 0;
		background: transparent;
	}
	:not(.head) > hr::before {
		content: "\2727\2003\2003\2727\2003\2003\2727";
	}

/******************************************************************************/
/*                            Paragraphs and Lists                            */
/******************************************************************************/

	p {
		margin: 1em 0;
	}

	dd > p:first-child,
	li > p:first-child {
		margin-top: 0;
	}

	ul, ol {
		margin-left: 0;
		padding-left: 2em;
	}

	li {
		margin: 0.25em 0 0.5em;
		padding: 0;
	}

	dl dd {
		margin: 0 0 .5em 2em;
	}

	.head dd + dd { /* compact for header */
		margin-top: -.5em;
	}

	/* Style for algorithms */
	ol.algorithm ol:not(.algorithm),
	.algorithm > ol ol:not(.algorithm) {
	 border-left: 0.5em solid #DEF;
	}

	/* Put nice boxes around each algorithm. */
	[data-algorithm]:not(.heading) {
	  padding: .5em;
	  border: thin solid #ddd; border-radius: .5em;
	  margin: .5em calc(-0.5em - 1px);
	}
	[data-algorithm]:not(.heading) > :first-child {
	  margin-top: 0;
	}
	[data-algorithm]:not(.heading) > :last-child {
	  margin-bottom: 0;
	}

	/* Style for switch/case <dl>s */
	dl.switch > dd > ol.only,
	dl.switch > dd > .only > ol {
	 margin-left: 0;
	}
	dl.switch > dd > ol.algorithm,
	dl.switch > dd > .algorithm > ol {
	 margin-left: -2em;
	}
	dl.switch {
	 padding-left: 2em;
	}
	dl.switch > dt {
	 text-indent: -1.5em;
	 margin-top: 1em;
	}
	dl.switch > dt + dt {
	 margin-top: 0;
	}
	dl.switch > dt::before {
	 content: '\21AA';
	 padding: 0 0.5em 0 0;
	 display: inline-block;
	 width: 1em;
	 text-align: right;
	 line-height: 0.5em;
	}

/** Terminology Markup ********************************************************/


/******************************************************************************/
/*                                 Inline Markup                              */
/******************************************************************************/

/** Terminology Markup ********************************************************/
	dfn   { /* Defining instance */
		font-weight: bolder;
	}
	a > i { /* Instance of term */
		font-style: normal;
	}
	dt dfn code, code.idl {
		font-size: medium;
	}
	dfn var {
		font-style: normal;
	}

/** Change Marking ************************************************************/

	del { color: red;  text-decoration: line-through; }
	ins { color: #080; text-decoration: underline;    }

/** Miscellaneous improvements to inline formatting ***************************/

	sup {
		vertical-align: super;
		font-size: 80%
	}

/******************************************************************************/
/*                                    Code                                    */
/******************************************************************************/

/** General monospace/pre rules ***********************************************/

	pre, code, samp {
		font-family: Menlo, Consolas, "DejaVu Sans Mono", Monaco, monospace;
		font-size: .9em;
		page-break-inside: avoid;
		hyphens: none;
		text-transform: none;
	}
	pre code,
	code code {
		font-size: 100%;
	}

	pre {
		margin-top: 1em;
		margin-bottom: 1em;
		overflow: auto;
	}

/** Inline Code fragments *****************************************************/

  /* Do something nice. */

/******************************************************************************/
/*                                    Links                                   */
/******************************************************************************/

/** General Hyperlinks ********************************************************/

	/* We hyperlink a lot, so make it less intrusive */
	a[href] {
		color: #034575;
		text-decoration: none;
		border-bottom: 1px solid #707070;
		/* Need a bit of extending for it to look okay */
		padding: 0 1px 0;
		margin: 0 -1px 0;
	}
	a:visited {
		border-bottom-color: #BBB;
	}

	/* Use distinguishing colors when user is interacting with the link */
	a[href]:focus,
	a[href]:hover {
		background: #f8f8f8;
		background: rgba(75%, 75%, 75%, .25);
		border-bottom-width: 3px;
		margin-bottom: -2px;
	}
	a[href]:active {
		color: #C00;
		border-color: #C00;
	}

	/* Backout above styling for W3C logo */
	.head .logo,
	.head .logo a {
		border: none;
		text-decoration: none;
		background: transparent;
	}

/******************************************************************************/
/*                                    Images                                  */
/******************************************************************************/

	img {
		border-style: none;
	}

	/* For autogen numbers, add
	   .caption::before, figcaption::before { content: "Figure " counter(figure) ". "; }
	*/

	figure, .figure, .sidefigure {
		page-break-inside: avoid;
		text-align: center;
		margin: 2.5em 0;
	}
	.figure img,    .sidefigure img,    figure img,
	.figure object, .sidefigure object, figure object {
		max-width: 100%;
		margin: auto;
	}
	.figure pre, .sidefigure pre, figure pre {
		text-align: left;
		display: table;
		margin: 1em auto;
	}
	.figure table, figure table {
		margin: auto;
	}
	@media screen and (min-width: 20em) {
		.sidefigure {
			float: right;
			width: 50%;
			margin: 0 0 0.5em 0.5em
		}
	}
	.caption, figcaption, caption {
		font-style: italic;
		font-size: 90%;
	}
	.caption::before, figcaption::before, figcaption > .marker {
		font-weight: bold;
	}
	.caption, figcaption {
		counter-increment: figure;
	}

	/* DL list is indented 2em, but figure inside it is not */
	dd > .figure, dd > figure { margin-left: -2em }

/******************************************************************************/
/*                             Colored Boxes                                  */
/******************************************************************************/

	.issue, .note, .example, .assertion, .advisement, blockquote {
		padding: .5em;
		border: .5em;
		border-left-style: solid;
		page-break-inside: avoid;
	}
	span.issue, span.note {
		padding: .1em .5em .15em;
		border-right-style: solid;
	}

	.issue,
	.note,
	.example,
	.advisement,
	.assertion,
	blockquote {
		margin: 1em auto;
	}
	.note  > p:first-child,
	.issue > p:first-child,
	blockquote > :first-child {
		margin-top: 0;
	}
	blockquote > :last-child {
		margin-bottom: 0;
	}

/** Blockquotes ***************************************************************/

	blockquote {
		border-color: silver;
	}

/** Open issue ****************************************************************/

	.issue {
		border-color: #E05252;
		background: #FBE9E9;
		counter-increment: issue;
		overflow: auto;
	}
	.issue::before, .issue > .marker {
		text-transform: uppercase;
		color: #AE1E1E;
		padding-right: 1em;
		text-transform: uppercase;
	}
	/* Add .issue::before { content: "Issue " counter(issue) " "; } for autogen numbers,
	   or use class="marker" to mark up the issue number in source. */

/** Example *******************************************************************/

	.example {
		border-color: #E0CB52;
		background: #FCFAEE;
		counter-increment: example;
		overflow: auto;
		clear: both;
	}
	.example::before, .example > .marker {
		text-transform: uppercase;
		color: #827017;
		min-width: 7.5em;
		display: block;
	}
	/* Add .example::before { content: "Example " counter(example) " "; } for autogen numbers,
	   or use class="marker" to mark up the example number in source. */

/** Non-normative Note ********************************************************/

	.note {
		border-color: #52E052;
		background: #E9FBE9;
		overflow: auto;
	}

	.note::before, .note > .marker,
	details.note > summary::before,
	details.note > summary > .marker {
		text-transform: uppercase;
		display: block;
		color: hsl(120, 70%, 30%);
	}
	/* Add .note::before { content: "Note"; } for autogen label,
	   or use class="marker" to mark up the label in source. */

	details.note > summary {
		display: block;
		color: hsl(120, 70%, 30%);
	}
	details.note[open] > summary {
		border-bottom: 1px silver solid;
	}

/** Assertion Box *************************************************************/
	/*  for assertions in algorithms */

	.assertion {
		border-color: #AAA;
		background: #EEE;
	}

/** Advisement Box ************************************************************/
	/*  for attention-grabbing normative statements */

	.advisement {
		border-color: orange;
		border-style: none solid;
		background: #FFEECC;
	}
	strong.advisement {
		display: block;
		text-align: center;
	}
	.advisement > .marker {
		color: #B35F00;
	}

/** Spec Obsoletion Notice ****************************************************/
	/* obnoxious obsoletion notice for older/abandoned specs. */

	details {
		display: block;
	}
	summary {
		font-weight: bolder;
	}

	.annoying-warning:not(details),
	details.annoying-warning:not([open]) > summary,
	details.annoying-warning[open] {
		background: #fdd;
		color: red;
		font-weight: bold;
		padding: .75em 1em;
		border: thick red;
		border-style: solid;
		border-radius: 1em;
	}
	.annoying-warning :last-child {
		margin-bottom: 0;
	}

@media not print {
	details.annoying-warning[open] {
		position: fixed;
		left: 1em;
		right: 1em;
		bottom: 1em;
		z-index: 1000;
	}
}

	details.annoying-warning:not([open]) > summary {
		text-align: center;
	}

/** Entity Definition Boxes ***************************************************/

	.def {
		padding: .5em 1em;
		background: #DEF;
		margin: 1.2em 0;
		border-left: 0.5em solid #8CCBF2;
	}

/******************************************************************************/
/*                                    Tables                                  */
/******************************************************************************/

	th, td {
		text-align: left;
		text-align: start;
	}

/** Property/Descriptor Definition Tables *************************************/

	table.def {
		/* inherits .def box styling, see above */
		width: 100%;
		border-spacing: 0;
	}

	table.def td,
	table.def th {
		padding: 0.5em;
		vertical-align: baseline;
		border-bottom: 1px solid #bbd7e9;
	}

	table.def > tbody > tr:last-child th,
	table.def > tbody > tr:last-child td {
		border-bottom: 0;
	}

	table.def th {
		font-style: italic;
		font-weight: normal;
		padding-left: 1em;
		width: 3em;
	}

	/* For when values are extra-complex and need formatting for readability */
	table td.pre {
		white-space: pre-wrap;
	}

	/* A footnote at the bottom of a def table */
	table.def           td.footnote {
		padding-top: 0.6em;
	}
	table.def           td.footnote::before {
		content: " ";
		display: block;
		height: 0.6em;
		width: 4em;
		border-top: thin solid;
	}

/** Data tables (and properly marked-up index tables) *************************/
	/*
		 <table class="data"> highlights structural relationships in a table
		 when correct markup is used (e.g. thead/tbody, th vs. td, scope attribute)

		 Use class="complex data" for particularly complicated tables --
		 (This will draw more lines: busier, but clearer.)

		 Use class="long" on table cells with paragraph-like contents
		 (This will adjust text alignment accordingly.)
		 Alternately use class="longlastcol" on tables, to have the last column assume "long".
	*/

	table {
		word-wrap: normal;
		overflow-wrap: normal;
		hyphens: manual;
	}

	table.data,
	table.index {
		margin: 1em auto;
		border-collapse: collapse;
		border: hidden;
		width: 100%;
	}
	table.data caption,
	table.index caption {
		max-width: 50em;
		margin: 0 auto 1em;
	}

	table.data td,  table.data th,
	table.index td, table.index th {
		padding: 0.5em 1em;
		border-width: 1px;
		border-color: silver;
		border-top-style: solid;
	}

	table.data thead td:empty {
		padding: 0;
		border: 0;
	}

	table.data  thead,
	table.index thead,
	table.data  tbody,
	table.index tbody {
		border-bottom: 2px solid;
	}

	table.data colgroup,
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		border-left: 2px solid;
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	table.data  tbody th:first-child,
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		border-right: 2px solid;
		border-top: 1px solid silver;
		padding-right: 1em;
	}

	table.data th[colspan],
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	table.complex.data th,
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		text-align: center;
	}

	table.data.longlastcol td:last-child,
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	 vertical-align: baseline;
	 text-align: left;
	}

	table.data img {
		vertical-align: middle;
	}


/*
Alternate table alignment rules

	table.data,
	table.index {
		text-align: center;
	}

	table.data  thead th[scope="row"],
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		text-align: right;
	}

	table.data  tbody th:first-child,
	table.index tbody th:first-child  {
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Possible extra rowspan handling

	table.data  tbody th[rowspan]:not([rowspan='1']),
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	table.data  tbody td[rowspan]:not([rowspan='1']),
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	table.data  tbody th[rowspan]:first-child,
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	table.index tbody td[rowspan]:first-child{
		border-left: 0;
		border-right: 1px solid silver;
	}
*/

/******************************************************************************/
/*                                  Indices                                   */
/******************************************************************************/


/** Table of Contents *********************************************************/

	.toc a {
		/* More spacing; use padding to make it part of the click target. */
		padding-top: 0.1rem;
		/* Larger, more consistently-sized click target */
		display: block;
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		border-bottom-width: 3px !important;
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/** Index *********************************************************************/

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/** Index Tables *****************************************************/
	/* See also the data table styling section, which this effectively subclasses */

	table.index {
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		text-align: left;
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	table.index td,
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	}

/******************************************************************************/
/*                                    Print                                   */
/******************************************************************************/

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		/* Serif for print. */
		body {
			font-family: serif;
		}
	}
	@page {
		margin: 1.5cm 1.1cm;
	}

/******************************************************************************/
/*                                    Legacy                                  */
/******************************************************************************/

	/* This rule is inherited from past style sheets. No idea what it's for. */
	.hide { display: none }



/******************************************************************************/
/*                             Overflow Control                               */
/******************************************************************************/

	.figure .caption, .sidefigure .caption, figcaption {
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		margin-left: auto;
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	}
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<style>/* style-md-lists */

/* This is a weird hack for me not yet following the commonmark spec
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<style>/* style-var-click-highlighting */

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pre .property::before, pre .property::after {
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[data-link-type="property"]::before,
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</style>
 <body class="h-entry">
  <div class="head">
   <p data-fill-with="logo"></p>
   <h1 class="p-name no-ref" id="title">Private Click Measurement</h1>
   <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Draft Community Group Report, <time class="dt-updated" datetime="1970-01-01">1 January 1970</time></span></h2>
   <div data-fill-with="spec-metadata">
    <dl>
     <dt>This version:
     <dd><a class="u-url" href="https://wicg.github.io/ad-click-attribution/index.html">https://wicg.github.io/ad-click-attribution/index.html</a>
     <dt class="editor">Editors:
     <dd class="editor p-author h-card vcard"><a class="p-name fn u-email email" href="mailto:wilander@apple.com">John Wilander</a> (<a class="p-org org" href="https://apple.com/">Apple Inc.</a>)
     <dd class="editor p-author h-card vcard"><a class="p-name fn u-email email" href="mailto:jnovak@apple.com">Jason Novak</a> (<a class="p-org org" href="https://apple.com/">Apple Inc.</a>)
    </dl>
   </div>
   <div data-fill-with="warning"></div>
   <p class="copyright" data-fill-with="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> © 1970 the Contributors to the Private Click Measurement Specification, published by the <a href="https://www.w3.org/community/wicg/">Web Platform Incubator Community Group</a> under the <a href="https://www.w3.org/community/about/agreements/cla/">W3C Community Contributor License Agreement (CLA)</a>.
A human-readable <a href="http://www.w3.org/community/about/agreements/cla-deed/">summary</a> is available. </p>
   <hr title="Separator for header">
  </div>
  <div class="p-summary" data-fill-with="abstract">
   <h2 class="no-num no-toc no-ref heading settled" id="abstract"><span class="content">Abstract</span></h2>
   <p>This specification defines a privacy preserving way to attribute a conversion, such as a purchase or a sign-up, to a previous ad click.</p>
  </div>
  <div data-fill-with="at-risk"></div>
  <h2 class="no-num no-toc no-ref heading settled" id="status"><span class="content">Status of this document</span></h2>
  <div data-fill-with="status">
   <p> This specification was published by the <a href="https://www.w3.org/community/wicg/">Web Platform Incubator Community Group</a>.
  It is not a W3C Standard nor is it on the W3C Standards Track.

  Please note that under the <a href="https://www.w3.org/community/about/agreements/cla/">W3C Community Contributor License Agreement (CLA)</a> there is a limited opt-out and other conditions apply.

  Learn more about <a href="http://www.w3.org/community/">W3C Community and Business Groups</a>. </p>
   <p></p>
  </div>
  <div data-fill-with="at-risk"></div>
  <nav data-fill-with="table-of-contents" id="toc">
   <h2 class="no-num no-toc no-ref" id="contents">Table of Contents</h2>
   <ol class="toc" role="directory">
    <li>
     <a href="#introduction"><span class="secno">1</span> <span class="content">Introduction</span></a>
     <ol class="toc">
      <li><a href="#goals"><span class="secno">1.1</span> <span class="content">Goals</span></a>
      <li><a href="#terminology"><span class="secno">1.2</span> <span class="content">Terminology</span></a>
      <li><a href="#scenario"><span class="secno">1.3</span> <span class="content">A High Level Scenario</span></a>
     </ol>
    <li><a href="#linkformat"><span class="secno">2</span> <span class="content">Ad Click Source Link Format</span></a>
    <li><a href="#legacytriggering"><span class="secno">3</span> <span class="content">Legacy Triggering of Ad Click Attribution</span></a>
    <li><a href="#moderntriggering"><span class="secno">4</span> <span class="content">Modern Triggering of Ad Click Attribution</span></a>
    <li><a href="#privacy"><span class="secno">5</span> <span class="content">Privacy Considerations</span></a>
    <li><a href="#performance"><span class="secno">6</span> <span class="content">Performance Considerations</span></a>
    <li><a href="#relatedwork"><span class="secno">7</span> <span class="content">Related Work</span></a>
    <li><a href="#acknowledgements"><span class="secno">8</span> <span class="content">Acknowledgements</span></a>
    <li><a href="#conformance"><span class="secno"></span> <span class="content"> Conformance</span></a>
    <li>
     <a href="#index"><span class="secno"></span> <span class="content">Index</span></a>
     <ol class="toc">
      <li><a href="#index-defined-here"><span class="secno"></span> <span class="content">Terms defined by this specification</span></a>
      <li><a href="#index-defined-elsewhere"><span class="secno"></span> <span class="content">Terms defined by reference</span></a>
     </ol>
    <li>
     <a href="#references"><span class="secno"></span> <span class="content">References</span></a>
     <ol class="toc">
      <li><a href="#normative"><span class="secno"></span> <span class="content">Normative References</span></a>
     </ol>
    <li><a href="#idl-index"><span class="secno"></span> <span class="content">IDL Index</span></a>
    <li><a href="#issues-index"><span class="secno"></span> <span class="content">Issues Index</span></a>
   </ol>
  </nav>
  <main>
   <h2 class="heading settled" data-level="1" id="introduction"><span class="secno">1. </span><span class="content">Introduction</span><a class="self-link" href="#introduction"></a></h2>
   <p><em>This section is non-normative.</em></p>
   <p>A popular business model for the web is to get attribution and payment for conversions, for instance purchases or sign-ups, which result from the click on an ad. Traditionally, such attribution has been facilitated by user identifying cookies sent in third-party HTTP requests to the click source. However, the same technology can be and has been used for privacy invasive cross-site tracking of users.</p>
   <p>The technology described in this document is intended to allow for ad click attribution while disallowing arbitrary cross-site tracking.</p>
   <h3 class="heading settled" data-level="1.1" id="goals"><span class="secno">1.1. </span><span class="content">Goals</span><a class="self-link" href="#goals"></a></h3>
   <ul>
    <li data-md>
     <p>Support ad click attribution.</p>
    <li data-md>
     <p>Preserve user privacy, specifically prevent cross-site tracking of users.</p>
   </ul>
   <h3 class="heading settled" data-level="1.2" id="terminology"><span class="secno">1.2. </span><span class="content">Terminology</span><a class="self-link" href="#terminology"></a></h3>
   <ul>
    <li data-md>
     <p><b>Ad click.</b> This document will use the term “ad click” for any kind of user gesture on an ad that invokes the navigation to a link destination, such as clicks, taps, and accessibility tools.</p>
    <li data-md>
     <p><b>Conversion.</b> A user activity that is notable such as a purchase, a sign-up to a service, or the submission of personal information such as an email address.</p>
   </ul>
   <p>The four parties involved in this technology are:</p>
   <ul>
    <li data-md>
     <p><b>The user.</b> They click on an ad, end up on a destination website, and perform what’s deemed to be a conversion, such as a purchase.</p>
    <li data-md>
     <p><b>The user agent.</b> The web browser that acts on behalf of the user and facilitates ad click attribution.</p>
    <li data-md>
     <p><b>The ad click source.</b> The first-party website where the user clicks on the ad.</p>
    <li data-md>
     <p><b>The ad click destination.</b> The destination website where the conversion happens.</p>
   </ul>
   <p>The data consumed by the user agent to support ad click attribution is:</p>
   <ul>
    <li data-md>
     <p><b>Ad Campaign Id.</b> A 6-bit decimal identifier for an ad campaign associated with the ad click destination. This means support for 64 concurrent ad campaigns per ad click destination on the ad click source. Example: merchant.example can run up to 64 concurrent ad campaigns on search.example. The valid decimal values are 00 to 63.</p>
    <li data-md>
     <p><b>Ad Attribution Data.</b> A 6-bit decimal value encoding the details of the attribution. This data may contain things like specific steps in a sales funnel or the value of the sale in buckets, such as less than $10, between $10 and $50, between $51 and $200, above $200, and so on. The valid decimal values are 00 to 63.</p>
    <li data-md>
     <p><b>Ad Attribution Priority.</b> An optional 6-bit decimal value encoding the priority of the attribution. The priority is only intended for the user agent to be able to pick the most important attribution request if there are multiple. One such case may be after the user has taken step 1 through 3 in a sales funnel and the third step is the most important to get attribution for. The valid decimal values are 00 to 63.</p>
   </ul>
   <h3 class="heading settled" data-level="1.3" id="scenario"><span class="secno">1.3. </span><span class="content">A High Level Scenario</span><a class="self-link" href="#scenario"></a></h3>
   <p>A high level example of a scenario where the described technology is intended to come into play is this:</p>
   <ol>
    <li data-md>
     <p>The user makes an online search on search.example’s website.</p>
    <li data-md>
     <p>The user is shown an ad for a product and clicks it.</p>
    <li data-md>
     <p>The ad click source informs the user agent:</p>
     <ul>
      <li data-md>
       <p>That it will want ad click attribution for this click.</p>
      <li data-md>
       <p>What the intended ad click destination is.</p>
      <li data-md>
       <p>What the attribution campaign id is.</p>
     </ul>
    <li data-md>
     <p>The user agent navigates the link and takes note that the user landed on the intended ad click destination.</p>
    <li data-md>
     <p>The user’s activity on the ad click destination leads to a conversion.</p>
    <li data-md>
     <p>A third-party HTTP request is made on the ad click destination website to ​https://search.example/.well-known/ad-click-attribution</p>
    <li data-md>
     <p>The user agent checks for pending ad click attributions for the ad click source/destination pair and if there’s a hit, makes or schedules an HTTP request to ​https://search.example/.well-known/ad-click-attribution with the ad click attribution data. One thing to consider here is whether there should be an option to send the attribution data to the ad click destination too.</p>
   </ol>
   <h2 class="heading settled" data-level="2" id="linkformat"><span class="secno">2. </span><span class="content">Ad Click Source Link Format</span><a class="self-link" href="#linkformat"></a></h2>
   <p>The ad click source needs to be an anchor tag with the following properties:</p>
<pre class="highlight"><c- p>&lt;</c-><c- f>a</c-> <c- e>adCampaignId</c-><c- o>=</c-><c- s>"[6-bit ad campaign id]"</c-> <c- e>adDestination</c-><c- o>=</c-><c- s>"[ad click destination URL]"</c-><c- p>></c->
</pre>
   <p>Formally:</p>
<pre class="idl highlight def"><c- b>partial</c-> <c- b>interface</c-> <a class="idl-code" data-link-type="interface" href="https://html.spec.whatwg.org/multipage/text-level-semantics.html#htmlanchorelement" id="ref-for-htmlanchorelement"><c- g>HTMLAnchorElement</c-></a> {
    [<a class="idl-code" data-link-type="extended-attribute" href="https://html.spec.whatwg.org/multipage/custom-elements.html#cereactions" id="ref-for-cereactions"><c- g>CEReactions</c-></a>=<a class="n" data-link-type="idl-name"><c- n>NotNeeded</c-></a>, <a class="idl-code" data-link-type="extended-attribute"><c- g>Reflect</c-></a>] <c- b>attribute</c-> <a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-DOMString" id="ref-for-idl-DOMString"><c- b>DOMString</c-></a> <dfn class="idl-code" data-dfn-for="HTMLAnchorElement" data-dfn-type="attribute" data-export data-type="DOMString" id="dom-htmlanchorelement-adcampaignid"><code><c- g>adCampaignId</c-></code><a class="self-link" href="#dom-htmlanchorelement-adcampaignid"></a></dfn>;
    [<a class="idl-code" data-link-type="extended-attribute" href="https://html.spec.whatwg.org/multipage/custom-elements.html#cereactions" id="ref-for-cereactions①"><c- g>CEReactions</c-></a>=<a class="n" data-link-type="idl-name"><c- n>NotNeeded</c-></a>, <a class="idl-code" data-link-type="extended-attribute"><c- g>Reflect</c-></a>] <c- b>attribute</c-> <a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-DOMString" id="ref-for-idl-DOMString①"><c- b>DOMString</c-></a> <dfn class="idl-code" data-dfn-for="HTMLAnchorElement" data-dfn-type="attribute" data-export data-type="DOMString" id="dom-htmlanchorelement-addestination"><code><c- g>adDestination</c-></code><a class="self-link" href="#dom-htmlanchorelement-addestination"></a></dfn>;
};
</pre>
   <p class="issue" id="issue-c9234009"><a class="self-link" href="#issue-c9234009"></a> These attributes should be on HTMLHyperlinkElementUtils instead.</p>
   <p>If an ad click on the above link triggers a top frame navigation that lands, possibly after HTTP redirects, on the <code>[ad click destination eTLD+1]</code>, the user agent stores the request for ad click attribution as the triple <code>{ [ad click source eTLD+1], [ad click destination eTLD+1], [6-bit ad campaign id] }</code>. If any of the conditions do not hold, such as the ad campaign id being larger than 6-bit, the request for ad click attribution is ignored.</p>
   <h2 class="heading settled" data-level="3" id="legacytriggering"><span class="secno">3. </span><span class="content">Legacy Triggering of Ad Click Attribution</span><a class="self-link" href="#legacytriggering"></a></h2>
   <p>Triggering of attribution is what happens when there is a conversion.</p>
   <p>Existing ad click attribution relies on third-party HTTP requests to the click source and these requests are typically the result of invisible image elements or "tracking pixels" placed in the DOM solely to fire HTTP GET requests. To allow for a smooth transition from these old pixel requests to the new Ad Click Attribution technology, we propose a server-side redirect to a well-known <a data-link-type="biblio" href="#biblio-well-known">[WELL-KNOWN]</a> location as a legacy triggering mechanism.</p>
   <p>To make an existing pixel request an ad click attribution from the user agent, the top frame context of an ad click destination page needs to do the following:</p>
   <div class="algorithm" data-algorithm="legacy triggering of ad click attribution">
    <ol>
     <li data-md>
      <p>An HTTP GET request to the <code><var>ad click source eTLD+1</var></code>. This HTTP request may be the result of an HTTP redirect, such as searchUK.example HTTP 302 redirect to search.example. The use of HTTP GET is intentional in that existing “pixel requests” can be repurposed for this and in that the HTTP request should be idempotent.</p>
     <li data-md>
      <p>A secure HTTP GET redirect to <code><var>ad click source eTLD+1</var>/.well-known/ad-click-attribution/<var>6-bit ad attribution data</var>/<var>optional 6-bit ad attribution priority</var></code>. This ensures that the <code><var>ad click source eTLD+1</var></code> is in control of who can trigger click attribution on its behalf and optionally what the priority of the attribution is. If the user agent gets such an HTTP request, it will check its stored requests for click attribution, and if there’s a match for <code><var>ad click source eTLD+1</var>, <var>ad click destination eTLD+1</var></code>, it will make or schedule a secure HTTP POST request to <code><var>ad click source eTLD+1</var>/.well-known/ad-click-attribution/<var>6-bit ad attribution data</var>/<var>6-bit ad campaign id</var></code> with the referer header set to <code><var>ad click destination eTLD+1</var></code>. The use of HTTP POST is intentional in that it differs from the HTTP GET redirect used to trigger the attribution and in that it is not expected to be idempotent. If any of the conditions do not hold, such as the ad attribution data being larger than 6-bit, the request for ad click attribution is ignored. We may have to add a nonce to the HTTP POST request to prohibit double counting in cases where the user agent decides to retry the request.</p>
    </ol>
   </div>
   <p>If there are multiple ad click attribution requests for the same « [ad click source eTLD+1], [ad click destination eTLD+1] » pair, the one with the highest Ad Attribution Priority will be the one sent and the rest discarded.</p>
   <p class="issue" id="issue-3bd5b5fa"><a class="self-link" href="#issue-3bd5b5fa"></a> This needs to be reworked to monkeypatch HTML’s "follows a hyperlink" algorithm.</p>
   <h2 class="heading settled" data-level="4" id="moderntriggering"><span class="secno">4. </span><span class="content">Modern Triggering of Ad Click Attribution</span><a class="self-link" href="#moderntriggering"></a></h2>
   <p>We envision a JavaScript API that is called on an ad click destination page as a modern means to trigger attribution at a conversion. This API call removes the necessity for third-party "pixels" which is great for ad click sources who do not want to be third party resources.</p>
   <h2 class="heading settled" data-level="5" id="privacy"><span class="secno">5. </span><span class="content">Privacy Considerations</span><a class="self-link" href="#privacy"></a></h2>
   <p>The total entropy in ad click attribution HTTP requests is 12 bits (6+6), which means 4096 unique values can be managed for each pair of ad click source and ad click destination.</p>
   <p>With no other means of cross-site tracking, neither the ad click source nor the ad click destination will know whether the user has clicked an associated ad or not when a conversion happens. This restricts the entropy under control to 6 bits at any moment.</p>
   <p>Even if the ad click source and/or the ad click destination were to be in control of both pieces of 6-bit data, the total is 12 bits or 4096 unique values.</p>
   <p>We believe these restrictions avoid general cross-site tracking while still providing useful ad click attribution at web scale.</p>
   <p>In the interest of user privacy, user agents are encouraged to deploy the following restrictions to when and how they make secure HTTP POST requests to <code><var>[ad click source eTLD+1]</var>/.well-known/ad-click-attribution/<var>[6-bit ad attribution data]</var>/<var>[6-bit ad campaign id]</var></code>:</p>
   <ul>
    <li data-md>
     <p>The user agent targets a delay of ad click attribution requests by 24-48 hours. However, the user agent might not be running or the user’s device may be or disconnected from the Internet, in which case the request may be delayed further.</p>
    <li data-md>
     <p>The user agent only holds on to the triple <code>{ <var>[ad click source eTLD+1]</var>, <var>[ad click destination eTLD+1]</var>, <var>[6-bit ad campaign id]</var> }</code> for 7 days, i.e. one week of potential ad click attribution.</p>
    <li data-md>
     <p>The user agent doesn’t guarantee any specific order in which multiple ad click attribution requests for the same ad click destination are sent, since the order itself could be abused to increase the entropy.</p>
    <li data-md>
     <p>The user agent uses an ephemeral session (a.k.a. private or incognito mode) to make ad click attribution requests.</p>
    <li data-md>
     <p>The user agent doesn’t use or accept any credentials such as cookies, client certificates, or Basic Authentication in ad click attribution requests.</p>
    <li data-md>
     <p>The user agent may use a central clearinghouse to further anonymize ad click attribution requests, should a trustworthy clearinghouse exist.</p>
    <li data-md>
     <p>The user agent offers users a way to turn ad click attribution on and off. The default setting is on to encourage businesses to move to this technology and abandon general cross-site tracking.</p>
    <li data-md>
     <p>The user agent doesn’t support ad click attribution in private/incognito mode.</p>
   </ul>
   <h2 class="heading settled" data-level="6" id="performance"><span class="secno">6. </span><span class="content">Performance Considerations</span><a class="self-link" href="#performance"></a></h2>
   <p>The user agent may want to limit the amount of stored ad click attribution data. Limitations can be set per ad click source, per ad click destination, and on the total amount of ad click attribution data.</p>
   <h2 class="heading settled" data-level="7" id="relatedwork"><span class="secno">7. </span><span class="content">Related Work</span><a class="self-link" href="#relatedwork"></a></h2>
   <p>The Web Advertising Business Group has related work that started in January 2019. It similarly uses a .well-known path with no cookies.<br> <a href="https://github.com/w3c/web-advertising/blob/master/admetrics.md">https://github.com/w3c/web-advertising/blob/master/admetrics.md</a></p>
   <p>Brave publised a security and privacy model for ad confirmations in March 2019.<br> <a href="https://github.com/brave/brave-browser/wiki/Security-and-privacy-model-for-ad-confirmations">https://github.com/brave/brave-browser/wiki/Security-and-privacy-model-for-ad-confirmations</a></p>
   <p>Google Chrome published an explainer document on May 22, 2019, for a very similar technology. They cross-reference this spec in its earlier form on the WebKit wiki.<br> <a href="https://github.com/csharrison/conversion-measurement-api">https://github.com/csharrison/conversion-measurement-api</a></p>
   <h2 class="heading settled" data-level="8" id="acknowledgements"><span class="secno">8. </span><span class="content">Acknowledgements</span><a class="self-link" href="#acknowledgements"></a></h2>
   <p>Thanks to
Maciej Stachowiak,
Brent Fulgham,
Erik Neuenschwander,
Mark Xue,
Steven Englehardt,
and Ehsan Akghari,
for their feedback on this proposal.</p>
  </main>
  <div data-fill-with="conformance">
   <h2 class="no-ref no-num heading settled" id="conformance"><span class="content"> Conformance</span><a class="self-link" href="#conformance"></a></h2>
   <p> Conformance requirements are expressed with a combination of descriptive assertions and RFC 2119 terminology.
            The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL”
            in the normative parts of this document
            are to be interpreted as described in RFC 2119.
            However, for readability,
            these words do not appear in all uppercase letters in this specification. </p>
   <p> All of the text of this specification is normative
            except sections explicitly marked as non-normative, examples, and notes. <a data-link-type="biblio" href="#biblio-rfc2119">[RFC2119]</a> </p>
   <p> Examples in this specification are introduced with the words “for example”
            or are set apart from the normative text with <code>class="example"</code>, like this: </p>
   <div class="example" id="example-example"><a class="self-link" href="#example-example"></a> This is an example of an informative example. </div>
   <p> Informative notes begin with the word “Note”
            and are set apart from the normative text with <code>class="note"</code>, like this: </p>
   <p class="note" role="note"> Note, this is an informative note. </p>
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  <h2 class="no-num no-ref heading settled" id="index"><span class="content">Index</span><a class="self-link" href="#index"></a></h2>
  <h3 class="no-num no-ref heading settled" id="index-defined-here"><span class="content">Terms defined by this specification</span><a class="self-link" href="#index-defined-here"></a></h3>
  <ul class="index">
   <li><a href="#dom-htmlanchorelement-adcampaignid">adCampaignId</a><span>, in §2</span>
   <li><a href="#dom-htmlanchorelement-addestination">adDestination</a><span>, in §2</span>
  </ul>
  <aside class="dfn-panel" data-for="term-for-cereactions">
   <a href="https://html.spec.whatwg.org/multipage/custom-elements.html#cereactions">https://html.spec.whatwg.org/multipage/custom-elements.html#cereactions</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-cereactions">2. Ad Click Source Link Format</a> <a href="#ref-for-cereactions①">(2)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-htmlanchorelement">
   <a href="https://html.spec.whatwg.org/multipage/text-level-semantics.html#htmlanchorelement">https://html.spec.whatwg.org/multipage/text-level-semantics.html#htmlanchorelement</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-htmlanchorelement">2. Ad Click Source Link Format</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-idl-DOMString">
   <a href="https://heycam.github.io/webidl/#idl-DOMString">https://heycam.github.io/webidl/#idl-DOMString</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-idl-DOMString">2. Ad Click Source Link Format</a> <a href="#ref-for-idl-DOMString①">(2)</a>
   </ul>
  </aside>
  <h3 class="no-num no-ref heading settled" id="index-defined-elsewhere"><span class="content">Terms defined by reference</span><a class="self-link" href="#index-defined-elsewhere"></a></h3>
  <ul class="index">
   <li>
    <a data-link-type="biblio">[HTML]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-cereactions" style="color:initial">CEReactions</span>
     <li><span class="dfn-paneled" id="term-for-htmlanchorelement" style="color:initial">HTMLAnchorElement</span>
    </ul>
   <li>
    <a data-link-type="biblio">[WebIDL]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-idl-DOMString" style="color:initial">DOMString</span>
    </ul>
  </ul>
  <h2 class="no-num no-ref heading settled" id="references"><span class="content">References</span><a class="self-link" href="#references"></a></h2>
  <h3 class="no-num no-ref heading settled" id="normative"><span class="content">Normative References</span><a class="self-link" href="#normative"></a></h3>
  <dl>
   <dt id="biblio-html">[HTML]
   <dd>Anne van Kesteren; et al. <a href="https://html.spec.whatwg.org/multipage/">HTML Standard</a>. Living Standard. URL: <a href="https://html.spec.whatwg.org/multipage/">https://html.spec.whatwg.org/multipage/</a>
   <dt id="biblio-rfc2119">[RFC2119]
   <dd>S. Bradner. <a href="https://tools.ietf.org/html/rfc2119">Key words for use in RFCs to Indicate Requirement Levels</a>. March 1997. Best Current Practice. URL: <a href="https://tools.ietf.org/html/rfc2119">https://tools.ietf.org/html/rfc2119</a>
   <dt id="biblio-webidl">[WebIDL]
   <dd>Boris Zbarsky. <a href="https://heycam.github.io/webidl/">Web IDL</a>. 15 December 2016. ED. URL: <a href="https://heycam.github.io/webidl/">https://heycam.github.io/webidl/</a>
   <dt id="biblio-well-known">[WELL-KNOWN]
   <dd>M. Nottingham. <a href="https://tools.ietf.org/html/rfc8615">Well-Known Uniform Resource Identifiers (URIs)</a>. May 2019. Proposed Standard. URL: <a href="https://tools.ietf.org/html/rfc8615">https://tools.ietf.org/html/rfc8615</a>
  </dl>
  <h2 class="no-num no-ref heading settled" id="idl-index"><span class="content">IDL Index</span><a class="self-link" href="#idl-index"></a></h2>
<pre class="idl highlight def"><c- b>partial</c-> <c- b>interface</c-> <a class="idl-code" data-link-type="interface" href="https://html.spec.whatwg.org/multipage/text-level-semantics.html#htmlanchorelement" id="ref-for-htmlanchorelement①"><c- g>HTMLAnchorElement</c-></a> {
    [<a class="idl-code" data-link-type="extended-attribute" href="https://html.spec.whatwg.org/multipage/custom-elements.html#cereactions" id="ref-for-cereactions②"><c- g>CEReactions</c-></a>=<a class="n" data-link-type="idl-name"><c- n>NotNeeded</c-></a>, <a class="idl-code" data-link-type="extended-attribute"><c- g>Reflect</c-></a>] <c- b>attribute</c-> <a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-DOMString" id="ref-for-idl-DOMString②"><c- b>DOMString</c-></a> <a data-type="DOMString" href="#dom-htmlanchorelement-adcampaignid"><code><c- g>adCampaignId</c-></code></a>;
    [<a class="idl-code" data-link-type="extended-attribute" href="https://html.spec.whatwg.org/multipage/custom-elements.html#cereactions" id="ref-for-cereactions①①"><c- g>CEReactions</c-></a>=<a class="n" data-link-type="idl-name"><c- n>NotNeeded</c-></a>, <a class="idl-code" data-link-type="extended-attribute"><c- g>Reflect</c-></a>] <c- b>attribute</c-> <a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-DOMString" id="ref-for-idl-DOMString①①"><c- b>DOMString</c-></a> <a data-type="DOMString" href="#dom-htmlanchorelement-addestination"><code><c- g>adDestination</c-></code></a>;
};

</pre>
  <h2 class="no-num no-ref heading settled" id="issues-index"><span class="content">Issues Index</span><a class="self-link" href="#issues-index"></a></h2>
  <div style="counter-reset:issue">
   <div class="issue"> These attributes should be on HTMLHyperlinkElementUtils instead.<a href="#issue-c9234009"> ↵ </a></div>
   <div class="issue"> This needs to be reworked to monkeypatch HTML’s "follows a hyperlink" algorithm.<a href="#issue-3bd5b5fa"> ↵ </a></div>
  </div>
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